1. Field of the Invention
This invention relates generally to the field of motor vehicle safety devices, and more specifically to a method and apparatus for monitoring a vehicle for potential overturn conditions. More particularly, the present invention concerns a method and apparatus for:
(1) determining and displaying the critical angle at which a vehicle is likely to overturn based on input vehicle and load information; PA0 (2) continuously monitoring and displaying the angle of the net dynamic forces on the vehicle during negotiation of the curve, including forces resulting from crosswind pressure, vehicle vertical acceleration, and vehicle lateral acceleration, for comparison with the displayed critical angle; PA0 (3) automatically comparing the net dynamic force vector with the critical angle and alerting the operator of the vehicle when the net dynamic force vector approaches the critical angle; and PA0 (4) enabling the operator of a vehicle to easily determine appropriate speeds for negotiating the curve based on the critical angle and the geometry of the curve, based on posted curve radii and bank information. PA0 (1) they fail to take into account the effect of variations in the center of gravity of a vehicle due to load, which can be especially significant in the case of large tractor/trailers, the critical roll over angle being a function of the center of gravity of the load, PA0 (2) they fail to provide a continuous display of the forces on the vehicle during negotiation of the curve, PA0 (3) they fail to relate those forces in a meaningful way to the critical roll over angle, and PA0 (4) there is no way to indicate to an operator of a vehicle the appropriate speed at which to enter the curve in order to avoid the danger of imminent roll over, because the appropriate speed depends on the vehicle characteristics and the radius and bank of the curve, which can not be determined by sensors before entering the curve.
2. Description of Related Art
Accidents involving vehicle roll overs cause significant economic losses and injuries to those involved in the roll overs, and to those caught in the resulting traffic back-ups. Vehicles which suffer from a high roll over likelihood include heavy trucks and sport utility vehicles with high centers of mass, as well as any high speed vehicle. In cases where a truck carrying hazardous materials is involved, the environmental damage can be irreparable, although an accident involving a sport utility vehicle carrying a family can be no less devastating to those involved.
At present, the only way to prevent such accidents is to rely on the skill and attention of the driver, but human error and, in the case of trucks, the need to transport the load to the intended destination as quickly as possible, coupled with driver fatigue or lack of training and poorly designed roadways, creates an ever present danger of such accidents. While road signs are commonly provided to indicate safe speed limits before corners, the road signs are usually based on automobiles, which have relatively low centers of mass, and are thus misleading for drivers of other vehicles. In addition, drivers often are not aware of where the resultant center of mass of their equipment/load is, there is no way for the typical driver to ascertain whether the equipment/load will present a problem in a corner, and crosswinds that might increase the possibility of an overturn are often undetected by the driver. Many temporary road surfaces, used while the main road is being prepared, have negative degrees of road bank with no warning. Generally, the driver has only the "feel" of the vehicle to ascertain overturn conditions. Often, if a rollover is imminent, it is too late to take corrective action.
It has previously been proposed to provide devices for indicating an imminent roll over. However, none provides a threshold indicator that takes into account all of the significant dynamic forces on the vehicle as well as such factors as the geometry of the load and of the roadway, all of which contribute to the likelihood of a roll over, much less a continuous display of the roll over inducing forces on the vehicle relative to the critical roll over angle or an indication of the appropriate speeds at which a curve should be entered in order to avoid approaching the critical angle. Generally, such devices are mounted outside the cab of the vehicle, leaving them exposed to the elements, and if the driver's attention is distracted, can easily be overlooked. None of the prior devices comes close to providing the operator of the vehicle with a useful way of relating roll over conditions to a critical roll over angle before a roll over occurs, so that the driver can take corrective action well in advance of a hazardous situation, and none provides a way of taking into account curve geometry, which is different for every curve, or load parameters.
The physics responsible for a roll over is of course known in general. Basically, there are four dynamic forces that act on the vehicle's center of mass, namely the force of gravity, the centrifugal force which is a function of the speed of the vehicle and the radius of the curve, an additional force resulting from air pressure or cross winds, and the effect of vehicle angular deflection from the suspension and tires. When the vector sum of the moments resulting from these forces, including the effect of vehicle angular deflection from the suspension and tires, approaches a critical angle determined by the position of the center of mass relative to the tires on the side of the vehicle in which the forces are directed, and the banking angle of the curve, the vehicle will roll over.
Knowing the effects of the forces of the vehicle in relation to vehicle geometry has not, however, led to a useful vehicle roll over indicator. Numerous problems must be overcome in order to provide an indicator that offers meaningful information to the operator, in the form that can be acted on to prevent a roll over, without distracting the attention of the vehicle operator from the task of driving, and without requiring the driver to make complex mental calculations or manipulate numerous controls. There is currently no way, for example, to automatically determine the banking of a curve, and no obvious way to allow a vehicle operator to factor the banking angle and vehicle geometry into the roll over equations. To display all of the individual factors that contribute to a roll over would overwhelm any vehicle operator and make the vehicle display panel resemble an aircraft cockpit, and yet to rely solely on dynamic sensors, such as sensors which measure deflection of the suspension of a vehicle as has previously been proposed, is to make it impossible to take into account variables such as curve radius and bank angle, and allow the driver to take corrective action.
Four problems with conventional overturn monitors are particularly intractible:
With respect to the first problem, while suspension and tire information, as well as vehicle unloaded mass and geometry can be determined and preset for a particular vehicle, load information cannot. Any device that takes into account the load information must enable entry of meaningful data which can be easily determined each time the vehicle is loaded, and which can be input into the device without an advanced degree in engineering or computer programming.
As to the second and third problems, while display of forces on a vehicle might in theory be possible, to do so in a meaningful way is quite another problem. In order for such a display to be useful, the display of dynamic forces on the vehicle would need to be related to the geometric factors that contribute to the roll over in a way that could be taken into account by the driver in a matter of seconds.
Furthermore, even though it may in theory be possible to construct a processor that uses vehicle information, once entered, to determine a critical angle, display the critical angle, and relate the critical angle to the forces on a vehicle in order to at least provide a threshold indication that a roll over is imminent during negotiation of a curve, it is currently impossible to use such information to determine a maximum safe speed in advance without knowledge of the curves. Once the radius of the curve is known, a machine could calculate and display the safe speed, but first the radius of the curve must be input to the calculator, which can at present only be done by the operator of the vehicle. It is of course possible for the driver of a vehicle to estimate the radius of a curve upon viewing the curve, and if there were a need to do so, it would be a simple and relatively inexpensive matter (compared to the cost of vehicle roll over accidents) for local officials to post the radius and bank of a dangerous curve, but it would be both impractical and unsafe for the operator to then have to input this information to the computer in order for the computer to calculate the safe speed while entering the curve, and there is no way that an operator of a vehicle could mentally calculate the maximum safe speed based on posted or estimated curve information and the vehicle geometry and center of mass. In order for curve information to be meaningful, the operator of the vehicle would still need a way to take into account the vehicle and load geometry and make a speed determination based on the vehicle and load geometry and posted curve information, which is basically impossible with previously proposed systems.
In general, therefore, all of the prior art roll over devices have involved simple on/off switching devices based on a threshold, without any attempt to provide for a continuous readout of the resultant force vector on the vehicle, establishing vehicle thresholds based on center of mass of vehicle/load or adjusting the threshold for vehicle and curve geometry, much less offering a visually suggested speed for a curve in anticipation of negotiating the curve below the overturn threshold, or a practical way to use posted curve information.